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Fatz you do have a couple of options here , first is to replace the .50 ARR comp cover with the larger .70 ARR T04E cover and keep the backplate .

Second is to use the larger series T04S cover and backplate (adapter ring) which is what Garrett did with their GT3540R turbocharger .

If your finances are limited go the larger ARR .70 "E" cover . If the sky is your limit go the "S" bits . Also remember that the T04S covers are quite large so make sure there's enough real estate where your turbo lives .

Generally compressor covers are sized around airflow rates or speed . So for a given compressor wheel the larger the Area Radius Ratio the lower the gas speed will be and vice versa . Also the larger it is the less chance it will have of being a choke point at high wheel speeds . Someone did tell me that all else being equal going up in comp cover AR brings the boost on a little later and "hits" harder .

With most Garrett turbos there is a set compressor wheel diameter for each wheel/cover family , ie 60mm wheels T3 covers , 71mm wheels T04B covers , 76mm wheels T04E covers , 82mm wheels T04S covers .

In recent years Garrett started going up a size in cover with some of the GT BB series compressors . I think this is because the comp wheels are mechanically stronger , and and can still pump efficiently at much higher rpm's than the bush bearing has beens . This is a win win situation , the small high speed wheels are compact , cheap to produce and more importantly have less innertia so spool sooner .

Examples of this are the little GT28RS (T04B comp cover) and some of the GT2835R series turbos with 71mm compressors and T04E covers .

The Garrett people inthe US tell me that the up sized cover , and a little extra tip height on the wheel , gives extra pumping capacity and a few more points compressor efficiency .

I can only think of two examples of Garrett turbos that went smaller in cover size , they are the HKS GT2540 and the Ford GT3540R . The 2540 is getting on and was probably an attempt to get a bit more flow and power out of a small series turbo , and a low mount compact (convienent) fit for GTR's .

Its safe to say Ford was not looking for serious performance with the XR6T so a compact and probably cheaper adequate cover got the nod . You can bet they knew people would modify them for performance , so the limited cover capacity may have been intended to limit the performance with the std turbo but not affect the standard state of tune .

Cheers A .

yea just stuck a side pipe on the beast and took it out to the drift day

sadly budget has died in the arse so i will have to putt around for some time until a set of cam gears arrive and the powerfc which is probably about 3 months away

im quite happy with the power but as soon as those cam gears are in hopefull it will bring it on a bit better

if cam gears dont bring it down to 4000rpm with power fc and a decent tune then i will consider the upgrade to external wastegate and a .86 rear housing and combine it with the larger front cover

but hey im happy as a pig in shit at the moment and when i win lotto ill do the next big upgrade

ive also got a rb30 complete engine that will be getting a solid bottom end over the next few years to replace the gtr bottom end when or if it ever goes

yea baby

anyone have some cheap cam gears

pete

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